Continuous plasma surface treatment method for elongated, flexible, clear polymeric tubing

ABSTRACT

A plasma treatment apparatus for treating elongated clear polymeric tubing, by moving the tubing through a plasma generation chamber and maintaining tension on the tubing below that at which clarity of the tubing is reduced.

This is a divisional of copending application Ser. No. 07/785,857 filedon Oct. 31, 1991, now U.S. Pat. No. 5,198,033.

BACKGROUND OF THE INVENTION

Treatment of substrates, particularly polymeric subtrates, with lowpressure ionized gases or "plasmas", has widely been reported to producealterations in the substrate surfaces which are desirable for certainapplications. For example, plasma treatment may reduce surface contactangles, improving wettability of the surface and/or bondability withcertain adhesives, and may also effect cross-linking of the substratematerial. Use of certain polymerizing gases may also allow thesubstrates to be coated with very thin layers of polymer. Other uses forplasma treatment are described in Gombotz et al, "Gas-DischargeTechniques For Biomaterial Modification", CRC Critical Reviews inBiocompatibility, 4, pp. 1-42 (1984).

In co-pending application Ser. No. 07/754,326, filed Sep. 4, 1991, as acontinuation of Ser. No. 07/457,019, filed Dec. 26, 1989, incorporatedherein by reference, it is disclosed that silicone rubber tubingemployed as a component of heart pacemaker leads has a tendency towardsurface blocking. Surface blocking is a phenomena which can result inadjacent implanted leads sticking to each other instead of movingindependently within the body, thereby increasing the risk ofdislodgment of the leads. The referenced application discloses thatplasma treatment of the silicone tubing used in forming such leadsreduces blocking, rendering pacemaker leads manufactured therefrom moreable to slip against each other within the body.

The present invention pertains to an apparatus which is particularlyuseful for treating implantable lead materials as described in Ser. No.07/754,326, but also has application for treatment of other strip-stockmaterial which may be desired to be plasma treated for any purpose. Theterm "strip-stock" as used herein is used generally to describematerials having very long lengths relative to their circumference andincludes flexible pipe and tubing, wire, filaments, strands, webs, andthe like.

Because of their relatively long length, strip-stock materials aregenerally unsuited for batch treatment processes in which the entirelength of the article is treated simultaneously in a vaccum chambercontaining a plasma. However, they may be located portion-wise bypushing or drawing the strip-stock material through a relatively shortplasma treatment chamber within a treatment apparatus until the entirelength has been treated. An apparatus for treating a roll of siliconetubing in this manner is disclosed in co-pending application Ser. No.07/754,326. In that application, a motor driven reel and pulley systemis used to draw a length of tubing from a feed reel into and through aplasma generated in a region of the apparatus and then winding thetubing up on a take-up reel as it comes out of the plasma generatingregion. The feed and take-up reels are located in a single evacuatedvessel fed with a suitable gas, the same vessel having a pair ofcapacitively coupled plates to a RF source, the space between the platesserving as the plasma generating region.

An alternative construction for treatment of strip-stock is thecommercially available PS1010 Plasma Treatment System, sold by PlasmaScience, of Foster City, Calif.

In working with silicone tubing treated in the manner described in Ser.No. 07/754,326, it was subsequently discovered that the treatmentprocess frequently produced reel-to-reel and place-to-place loss ofclarity of the tubing material. As little as 10% of the treated lengthof the roll of clear silicone tubing retained its original clarity usingthe apparatus of Ser. No. 07/754,326. This loss of clarity created aproblem in the manufacture of pacemaker leads, making it difficult toinspect the leads after assembly.

Investigations by the inventors of the present invention resulted in thediscovery that the loss of clarity problem is associated with the changein the topography of the surface of the substrate after treatment, andthe topography changes were attributable to differences in the tensionon the tubing within the plasma treatment zone of the apparatus fromtime to time. This last discovery has, in turn, now lead to thedevelopment of the instant invention as described herein.

SUMMARY OF THE INVENTION

In one aspect, the disclosed invention may be defined as a plasmatreatment apparatus including means for moving an elongated flexiblestrip-stock through a plasma gas within a plasma treatment region of theapparatus so as to effect plasma treatment of the surface of thestrip-stock material, the apparatus including tension maintenance meansfor maintaining tension on the strip-stock within a predetermined rangeas the strip-stock is moved through the plasma treatment region.

A particular apparatus within the scope of the invention includes avacuum chamber including a strip-stock storage area, a treated stockreceiving area and a plasma treatment area between said storage andreceiving areas; evacuation means for substantially evacuating thevacuum chamber; gas supply means for supplying a plasma generating gasto the plasma treatment region of the vacuum chamber at reducedpressure; plasma generating means for generating a plasma in the plasmatreatment region of the vacuum chamber; moving means for moving anelongated flexible strip-stock from the storage area through the plasmatreatment area to the receiving area; and tension maintenance means formaintaining tension on the strip-stock below a predetermined maximum asthe strip-stock is moved through the plasma treatment area.

In a further aspect, the invention may be described as a process forplasma treating an elongated flexible strip-stock material comprisinggenerating a plasma in a plasma generating chamber; moving thestrip-stock through the chamber at a predetermined speed to effectplasma treatment of the surface thereof; and maintaining tension on thestrip-stock within a predetermined range as the strip-stock is movedthrough the chamber.

The invention herein also encompasses novel treated strip-stockelastomeric polymer materials prepared by the inventive process andcharacterized by a substantially uniform surface topography over theentire length thereof.

DESCRIPTION OF THE FIGURES

FIG. 1 is a side elevational view of the present invention with partscut away;

FIG. 2 is a fragmentary sectional elevational view thereof taken alongline 2--2 of FIG. 1;

FIG. 3 is an enlarged detail of FIG. 1 with parts cut away showing thetension control mechanism of the inventive apparatus;

FIG. 4 is a fragmentary side elevational view of an alternate embodimentthereof employing a coupled capacitive plate RF generator.

FIG. 5 is a section thereof taken along line 5--5 of FIG. 4;

FIG. 6 is an exploded perspective view of an alternative embodiment ofthe vacuum chamber portion of the present invention;

FIG. 7 is a photomicrograph of the surface of a representative portionof silicone rubber tubing treated by the prior process of Ser. No.07/754,326; and

FIG. 8 is a photomicrograph of the surface of a representative portionof silicone rubber tubing treated in accordance with the inventiveprocess of the invention.

DETAILED DESCRIPTION OF THE INVENTION

In FIGS. 1-3, there is shown a preferred apparatus embodying theinvention hereof. The apparatus includes a vacuum chamber 10 whichcomprises a storage area 12, a plasma treatment region 14 and a treatedstock receiving area 16. Suitably the apparatus may be constructed froma pair of tee jars 20, 22 with a linear tubular segment 24 therebetween.O-ring seals 26, 27 are respectively situated between the tee jars andthe tubular segment 24. The bottoms of tee jars 20, 22 are sealed bybase members 28, 30 and O-rings 29, 31, respectively.

Jar ports 34, 36 of the tee jars are closed by end caps 38, 40 andassociated O-ring seals 39, 41.

Cap port 42 in end cap 38 provides connection to a vacuum source. Capport 44 in end cap 40 provides connection to a gas plasma supply,suitably a Nitrogen source.

An externally generated induction coil 50 connected to a RF powersource, not shown, provides means for generating plasma within theplasma treatment area 14.

Reel 52 rotatably mounted in the storage area of the vacuum chambercarries a roll of clear elastomeric polymer tubing 54 or otherstrip-stock material awaiting treatment. The tubing 54 is fed from reel52 into the plasma treatment area via pinch rollers 55, 56 and idlerroller 58 located in the proximal end of the plasma treatment region.Circular gear 60, engaged by worm gear 61 on the end of shaft 62, driveslower pinch roller 55. Shaft 62 is connected to a constant speed motor64 outside the vacuum chamber by a sealed feed through 65 so that thetubing is fed at constant speed into the plasma treatment region.

On the distal end of the plasma generating region of the vacuum chamberis a second idler roller 70 on the end of a journaled beam 74. A loadcell 76 is operatively mounted on beam 74 to detect the load applied tothe beam as the tubing 54 passes over roller 70. As tension on thetubing increases, the detected load increases. Consequently, the loadcell output is a signal indicative of the tension on tubing 54 withinthe plasma generation region.

From roller 70 the tubing passes out of the plasma into the storage area16 between pinch rollers 78, 80. Roller 78 connects motor 82 by afeedthrough and worm gear mechanism similar to the mechanism whichdrives roller 55. Motor 82 has a variable speed which is controlled by asuitable computer, not shown, which responds to the force details byload cell 76 so as to maintain the tension on tubing 54 within apredetermined range.

In alternative embodiments, not shown, the pinch rollers 55 and 78 maybe driven via an indirect connection, such as a belt and pulleyconnection which allows the roller speed to vary from a 1:1 ratio withthe motor speed.

After passing between pinch rollers 78, 80 the tubing is allowed to freefall into the storage area 16 allowing the treated tubing to relax toits unstressed condition.

FIGS. 4 and 5 depict a portion of the device of FIG. 1 employingalternative mechanism for plasma generation. In the device of thesefigures the induction coil surrounding the vacuum chamber has beenreplaced by external capacitively coupled plates 84, 86 connected to aRF source in a known manner. In still further alternatives, not shown,an inductive coil or a coupled capacitive plate assembly may be locatedon the inside of tubular segment 24 for plasma generation.

FIG. 6 depicts an alternative construction for the vacuum chamber inwhich the tee jars 20a and 22a located on either end of a tubularsegment 24 are provided with additional sealable ports 90, 92,respectively. Conveniently, the feed motor 64 feed through 65 of FIG. 1may be relocated to port 90 in this embodiment, with a correspondingrelocation of pinch rollers 55, 56, thereby providing easier removal ofthe base of jar 20a so as to facilitate loading of a new roll of tubinginto jar 20a. Similarly, the port 92 provides easier access forthreading the tubing over roller 70 of journaled beam 74 and betweenpinch rollers 78, 80.

The apparatus depicted in FIGS. 1-6 can generally be employed for anygoods deployable from a reel. Minor modifications will be necessary toutilize other packages, such as fan-folded sheets or center pull skeins.In the former case the reel may suitably be removed and the fan-foldedbundle simply placed on the base 29. In the latter case a suitable skeinretainer may need to be employed.

It will be appreciated by those skilled in the art that still otherstructural arrangements can be made to accomplish the tensionmaintenance and stock moving functions without departing from theinvention herein; for instance, reversing the location of the constantspeed and variable speed motors, using a reel drive rather than pinchrollers, etc.

Any gas already known for glow discharge may be used as well as mixturesof such gases. These gases are generally referred to as plasma gases andcan be grouped as nonpolymer forming and polymer-forming types. Typicalgases used in nonpolymer forming discharges are hydrogen, helium, argon,nitrogen, ammonia, carbon dioxide and, in special cases, C₂ F₆ which canexchange hydrogen and fluorine. Examples of polymer-forming gases are:C₂ F₄, C₃ F₆, C₂ H₄, C₂ H₂, CH₄, CH₂ CHCO₂ H, C₂ H₃ CONH₂, and amino orepoxy functional silanes.

Nitrogen, argon, helium, carbon dioxide, ammonia, oxygen, C₂ F₄, C₃ F₆,C₂ F₆ and combinations thereof are preferred. Particularly preferredgases for use alone or in various mixtures are argon, oxygen, helium,nitrogen, ammonia and carbon dioxide, nitrogen being most particularlypreferred.

Both nonpolymer-forming and polymer-forming plasma treatments of thesurface of silicone rubber reduce surface blocking. Plasma treatmentwith nonpolymer-forming gas is generally preferred.

The actual tension range employed will be determined empirically sincethe degree of topography modification varies with polymer material andother reaction parameters, such as gas pressure, line speed of thesubstrate material, gas flow rate and RF power. Preferably all of thereaction parameters are monitored and controlled by known means.Suitable tension ranges can readily be determined for given conditionsof these variables which provide acceptable and consistent treatment ofthe target substrate.

Moreover, the level of treatment sought may vary, depending upon theintended use for the substrate. For instance, in applications where thesurface is being prepared for subsequent adhesive bonding the objectivemay be to obtain a consistent treatment which will alter the topographyof the substrate, but which is insufficient to alter the dimensions,flexibility or other physical properties of the substrate material as awhole.

For a silicone rubber tubing substrate, such as Silastic® siliconetubing, treated to improve slip, typical reaction parameters in a 1meter-long reaction chamber, as shown in FIGS. 1-3, are as follows:

    ______________________________________                                        gas:                N.sub.2                                                   pressure:           40 millitorrs                                             line speed:         8.5 inches/min.                                           gas flow rate:      4 cc/min.                                                 RF power:           103 watts                                                 tension:            80 gm/meter.                                              ______________________________________                                    

These conditions provide optimal slip improvement (reduction ofblocking) without loss of clarity. A tension of as little as about 40gm/meter can still provide an adequate level of plasma treatment toprovide anti-slip under these flow rate pressue and power conditions,but a slower line speed may be required. A tension of 100 gm/meter wouldproduce loss of clarity under the same conditions unless line speed isincreased.

Whereas a 100-foot roll of clear silicone rubber tubing treated asdescribed herein, after treatment, provides substantially 100 feet ofusable product with undiminished clarity and a smooth topography, asshown in FIG. 7, the process and apparatus of Ser. No. 07/754,326provides approximately 10 feet of similarly useful product, theremaining product having a roughened surface topography, as shown inFIG. 8, which reduces the clarity of the tubing without furtherimproving the slip of the product.

This completes the description of the preferred and alternateembodiments of the invention. Those skilled in the art may recognizeother equivalents to the specific embodiment described herein whichequivalents are intended to be encompassed by the claims attachedhereto.

What is claimed is:
 1. A process for plasma treating an elongated,flexible, clear polymeric tubing material comprising:generating a plasmain a plasma generating chamber; moving the polymeric tubing through thechamber at a predetermined speed to effect plasma treating of thesurface thereof; maintaining tension on the tubing below a predeterminedlevel at which the clarity of the polymeric tubing is reduced by theplasma treatment.
 2. A process as in claim 1 wherein the polymerictubing is a clear silicone elastomeric tubing material.
 3. A process asin the claim 1 wherein the plasma is generated in a non-polymer forminggas selected from the group consisting of hydrogen, oxygen, helium,argon, nitrogen, ammonia, carbon dioxide and C₂ F₆.
 4. A process as inclaim 1 wherein the plasma is generated in a polymer forming gasselected from the group consisting of C₂ F₄ ; C₃ F₆ ; C₂ H₄ ; C₂ H₂ ;CH₄ ; CH₂ CHCO₂ H, C₂ H₃ CONH₂, and amino or epoxy functional silanes.5. A process as in claim 1 wherein the tension on the tubing ismaintained in a predetermined range by the steps of:measuring thetension applied to the tubing; and adjusting the tension applied to thetubing to within the predetermined range.